1. Field of the Invention
The present invention relates to a cooling structure which is disposed in a control unit mounted on a vehicle, such as a power distributor or an electric junction box, and which is used for cooling control semiconductor elements housed in a case of the control unit.
2. Description of the Related Art
Recently, semiconductor elements (particularly, switching elements) are widely used as means for performing various electronic controls in a vehicle. Usually, such semiconductor elements are housed in a protective case. Since semiconductor elements generate a relatively large amount of heat, semiconductor elements are preferably provided with a cooling structure which efficiently dissipates the generated heat to the outside of the case. A conventional known cooling structure is disclosed in, for example, JP-A-2000-92819. In the cooling structure, semiconductor elements in a case are connected to a heat sink member made of a metal in a heat transferable manner, the heat sink member is exposed to the outside of the case, and heat radiating fins are formed on an exposed face of the member. According to this structure, heat generated by the semiconductor elements is dissipated to the outside of the case through the heat sink member, and, in the outside of the case, the heat sink member and hence the semiconductor elements are efficiently cooled by traveling wind caused by a vehicle.
In the structure, the fins are formed integrally with the heat sink member, and the fins and the heat sink member are integrally formed by a metal. When end portions of the fins are exposed while leaving sharp edges to remain on the end portions, there arises a situation which is not preferable for safety reasons. As means for ensuring safety, it may be contemplated to chamfer the edges of the fins. In order to conduct such a chamfering work to a level at which safety is sufficiently attained, however, considerable labor is required. In the case where a large number of fins are formed, particularly, a long time period must be spent for the chamfering work. Therefore, this measure inevitably involves a large increase of the production cost.
The invention has been conducted in view of such circumstances, and therefore an object of the invention is to provide a cooling structure for a vehicle control unit in which semiconductor elements are efficiently cooled by using a heat sink member having fins, and safety of end portions of the fins can be sufficiently ensured by a simple structure that can be worked without requiring much labor.
To achieve the above problem, according to the invention, there is provided a cooling structure for a vehicle control unit in which semiconductor elements are housed in a case made of a resin, wherein a heat sink member which is connected to the semiconductor elements in a heat transferable manner is disposed on an outer face of the case, a plurality of fins are formed on a face of the heat sink member, the face being exposed to an outside of the case, and ribs having a thickness which is substantially equal to a thickness of the fins are formed on the outer face of the case, the ribs covering end portions of the fins in positions where the ribs are joined to the end portions of the fins, respectively.
According to this configuration, heat generated by the semiconductor elements in the case is guided to the outside of the case through the heat sink member, and then subjected to efficient heat exchange with the outside air by the fins formed on the heat sink member.
In this configuration, end portions of the fins are covered by the ribs which are protrudingly formed in the outside of the case, and hence fingers of the worker can be surely prevented from touching the end portions of the fins. Even when a precision chamfering work is not conducted on the end portions of the fins, therefore, high safety can be ensured by the ribs which are formed outside the end portions. Moreover, the ribs are formed into a fin-like shape having a thickness which is substantially equal to that of the fins of heat sink member, and in positions where the ribs are joined to the fins, respectively. Consequently, ventilation to spaces between the fins is satisfactorily maintained, so that there arises no fear that the cooling performance is impaired.
The disposing region and area of the heat sink member can be freely set. In order to improve the cooling performance, however, it is preferable to set the disposing area to be large. For example, a configuration may be employed in which the heat sink member is disposed over a region except end portions of the case in a predetermined direction, and the ribs are formed in the end portions of the case. According to this configuration, safety of the end portions of the fins can be ensured by the ribs while effectively increasing the area of the heat sink member.
In the invention, the fins may have any specific shape. In order to allow the fins to be easily worked, it is preferable to form the fins into a shape which is as simple as possible. When the fins are formed into a linear shape elongating in the predetermined direction, for example, the whole of the heat sink member can be formed by extrusion.
The cooling structure of the invention can be applied to a wide variety of control units which are mounted on a vehicle, and into which semiconductor elements are incorporated, and is particularly effective in the case where semiconductor elements generate a large amount of heat. When the vehicle control unit is a vehicle power distributor which distributes an electric power from a power source mounted on a vehicle, to a plurality of portions to be powered and the semiconductor elements are semiconductor switching elements which are respectively connected between the power source and the portions to be powered, currents of a considerably high level flow through the semiconductor elements to generate a large amount of heat. Therefore, the invention is preferably applied to a cooling structure for such a power distributor. Specifically, the semiconductor elements may be connected to a common heat sink member in a heat transferable manner, whereby an excellent cooling effect can be attained.